1. Field of the Invention
The present invention generally relates to a portable terminal including a smart phone, a tablet Personal Computer (PC), etc., and more particularly, to a device for improving the receiving sensitivity of a Long Term Evolution (LTE) antenna operating in an LTE band of low frequencies of 900 MHz or less.
2. Description of the Related Art
Portable terminals generally refer to information devices such as cellular phones, note books, smart phones, tablet Personal Computers (PCs), Personal Digital Assistants (PDAs), etc. In current multimedia environments, the growths of users of smart phones or tablet PCs are increasing due to convenient User Interface (UI) environments. The smart phone or the tablet PC provides not only general voice and text communications, but also various functions such as Internet, video streaming, personal schedule management, games, and so forth.
An exemplary smart phone 10 is shown in FIG. 1. As shown, a body housing 11 of the smart phone 10 includes a touch screen 12 on a front surface thereof, a camera 14 and a receiver 13 on an upper end portion thereof, and an on/off key 15 on a lower end portion thereof. At left and right sides with respect to the on/off key 15 are disposed a first touch area 16 and a second touch area 17. The first touch area 16 at the left side is a touch key for executing various particular functions, and the second touch area 17 at the right side is a touch key for executing a back function.
Referring to FIG. 2, a portable terminal/smart phone (10) has a display bracket 21 coupled in the body housing (11) thereof, and further includes a display device, various components, and a main Printed Circuit Board (PCB) (not shown) on top and bottom surfaces of the display bracket 21. First and second touch pads 26 and 27 and an on/off switch 25, which form a touch pad unit (30) disposed at an inner lower end of the body housing 11, are connected to the main PCB (not shown) through a Flexible PCB (FPCB).
As shown in FIGS. 3 and 4, as can be seen from a cross section of the touch pad unit (30), the touch pad unit (30) is formed of a touch pad layer 31 and a signal line layer/ground layer 32, i.e., as a two-layer thin structure in which upper and lower layers are attached to each other and stacked. The touch pad unit (30) is structure such that a Long Term Evolution (LTE) antenna A is disposed close to a bottom surface of the touch pad unit (30) and an LTE antenna feeding unit is disposed in the touch pad unit (30).
However, as shown in FIGS. 5 and 6, when a display device of a smart phone is in an on state, the touch pad unit 30 is operational at all times for sensing user's key input. As a result, low-frequency noise of an internal clock generated in a touch Integrated Circuit (IC) 35 included in the touch pad unit 30 leaks to outside through the touch pad unit 30, thus introducing the low-frequency noise to the antenna A. The arrows shown in FIGS. 5 and 6 represent directions in which the harmonic (low-frequency) noise generated in the touch IC 35 is delivered and leaks to the antenna A.
In particular, when an LTE Radio Frequency (RF) signal receives an RF signal in a low-frequency band such as 5 Band (869 MHz through 894 MHz), it is affected by noise of 24 MHz, thus lowering a receiving (RX) sensitivity level. The noise frequency band generated in the touch IC 35 is approximately 888 MHz (24 MHz×37), and the 5 Band LTE RX antenna band is approximately between 869 MHz and 894 MHz, thereby deteriorating the LTE antenna receiving sensitivity.